1. Field of the Invention
The present invention relates to a throttle controller attached to an internal combustion engine and, more particularly, to a throttle controller which has a means for opening and closing a throttle valve using a motor or the like in response to the operation of an accelerator pedal and also a driving control means for providing diverse kinds of control including constant speed drive control.
2. Description of the Prior Art
The throttle valve for an internal combustion engine regulates the mixture of fuel and air when installed inside the carburetor, or controls the quantity of air intake when incorporated in the electronically controlled fuel injector for control over engine output in conjunction with the accelerator operation system comprising an accelerator pedal.
The accelerator operation system used to be connected mechanically to the throttle valve. Recently, there have been proposed devices that open and close the throttle valve using a motor-driven or similar means in response to the accelerator pedal operation. One such device is disclosed in Japanese Patent Laid-open No. 55-145867. This device involves having the throttle valve connected to a step motor which is driven in response to the operation of the accelerator pedal.
With respect to such devices, Japanese Patent Laid-open No. 59-153945 proposes a number of prior art measures to be taken should a step motor-driven electrically controlled actuator become uncontrollable. One such measure is to disconnect the throttle shaft from the electronically controlled actuator by electromagnetic clutch and to return the throttle valve to its closed position by return spring. The proposals in the disclosure are based on the assumption that after control by the electronically controlled actuator has ceased, the lack of a means for operating the throttle valve necessarily makes it impossible to drive the vehicle even to nearby repair facilities.
More specifically, the disclosure in Japanese Patent Laid-open No. 59-153945 involves installing an electromagnetic clutch between rotation axis and throttle shaft. The rotation axis is rotated by stepping on the accelerator pedal. The electromagnetic clutch disconnects the rotation axis from the throttle shaft when excited, and connects the two when not excited. A control circuit detects errors that may occur in the control operation of the electronically controlled actuator and, in case of an error, stops supplying power to both the actuator and the electromagnetic clutch by means of a relay arrangement. If the actuator becomes uncontrollable, the throttle shaft is mechanically connected to the accelerator pedal via the electromagnetic clutch.
As indicated, the prior art contrivance disclosed in Japanese Patent Laid-open No. 59-153945 uses a separate control circuit to detect an inoperable state of the electronically controlled actuator; the control circuit stops the supply of power to both the actuator and the electromagnetic clutch. After control by the actuator has ceased, according to the disclosure, the rotation axis mechanically connected to the accelerator pedal gets coupled with the throttle shaft by means of the electromagnetic clutch. In an embodiment of the above-disclosed device, the motor does not generate any driving torque while the electronically controlled actuator is stopping its control. In that state, according to the disclosure, only a limited amount of stepping force is needed to operate the accelerator pedal which in turn adequately opens and closes the throttle valve. That is, the actuator remains coupled with the accelerator pedal after control is transferred thereto.
One disadvantage of using the electromagnetic clutch in such prior art equipment is that the clutch tends to be large in size, with its cost soaring correspondingly. Another disadvantage is that there might be a case, though not very likely, in which both the electronically controlled actuator and the control circuit malfunction at the same time. For example, an electronic interference can force the throttle valve to get stuck in its opened position. In such a case, even if a separate switching means stops the supply of power to the electromagnetic clutch so as to connect the throttle shaft to the accelerator pedal, there is no way of placing the throttle valve in the closed position; it then becomes difficult to maintain a desired opening of the throttle valve. In the above-described event, the driver of the vehicle will generally stop operating the accelerator pedal and apply the brakes. With the disclosed device, however, the throttle valve remains driven by the actuator.
To overcome these disadvantages, this applicant has proposed a novel throttle controller in Japanese Patent Appl. No. 1-22190. This throttle controller involves reliably disconnecting the driving means from the throttle valve if the operation of the accelerator pedal has ceased and if the throttle opening at that point in time is found in excess of a predetermined threshold of throttle opening. The arrangement thus stops control over the throttle valve by the driving source.
The above-mentioned throttle controller, too, requires a constant speed drive control function whereby the vehicle may travel at a constant speed without the operation of the accelerator pedal once the desired speed is set. This throttle controller in the application is constructed so that during vehicle run, the driving means is disconnected when the accelerator pedal operation is stopped. This makes it impossible to continue constant speed drive control. Thus there exists the need to have the driving source maintain control over the throttle valve even when the accelerator pedal is not operated.